1. Field of the Invention
The present invention relates to an inclination angle measurement apparatus that sends a wave toward a reflective object, such as a road surface, and measures an angle of inclination of a moving object (referred to as a vehicle from here on), such as a vehicle, aircraft, and magnetically-levitated linear motor car, with respect to the reflective object based on a phase difference between the phases of received waves reflected from the reflective object.
2. Description of Related Art
A prior art inclination angle measurement apparatus for measuring an angle of inclination of a vehicle is provided with two sensors disposed along the length of the vehicle, for simultaneously sending two ultrasonic waves toward a road surface, respectively, and for receiving ultrasonic waves reflected from the road surface, respectively so as to measure the angle of inclination of the vehicle with respect to the road surface based on a time difference between the times when the two sensors receive the ultrasonic waves reflected from the road surface (see Japanese patent application publication (TOKKAISHO) No. 56-8727).
A problem encountered with a prior art inclination angle measurement apparatus that is so constructed as to measure an angle of inclination of a vehicle with respect to a road surface based on a time difference between the times when two sensors receive ultrasonic waves reflected from the road surface is that because each received ultrasonic wave has small energy immediately after entering each of the two sensors and rises slowly in amplitude, the prior art inclination angle measurement apparatus cannot accurately detect the incident timing of the head of each of the two received ultrasonic waves. Therefore the prior art inclination angle measurement apparatus cannot accurately detect the time difference between the times when the two sensors receive the ultrasonic waves reflected from the road surface and cannot accurately measure the angle of inclination of the vehicle with respect to the road surface.